Pupil reflections reveal hidden faces behind the camera

Your eyes may be giving away more information than you would have ever imagined. A team of researchers in the Department of Psychology at the University of York has been taking a very close look at some photographs. Specifically, the team has been searching the eyes in photos for the reflections of those behind the camera.

The inky black of the pupil actually makes for a very good reflective surface — it’s like a black mirror. The researchers found that it was possible to recover low resolution images of faces from the reflection, but the faces were about 30,000 times smaller than the subject’s real face. The resolution of a reflected face at normal photo taking distance is exceedingly low — about 322 pixels for the entire thing.

The retrieved images were processed to smooth the pixels and ramp up the contrast to make the subject’s features more visible. These tiny thumbnails turned out to be amazingly good for identifying people despite the blurriness. We are all hardwired to recognize and remember faces, so even the suggestion of certain features can look like a face. In this case, there is enough data for people to recognize someone they know with 84% accuracy, according to the paper. In fact, even subjects not known to study participants were matched with real photos with 71% accuracy.

This is more than an interesting photographic quirk — it could be of use in police investigations. Any crime in which there are photos taken of a victim, like hostage situations or child abuse cases, could be combated with this method. Perpetrators rarely think to obscure their reflection in a victim’s eyes. Plus, it’s kind of fitting, right?

The University of York team also speculates that digital images of a more benign nature recovered during the course of an investigation could prove useful in developing a list of individuals linked to a suspect. Photographs could also be used to tie people to specific locations and times to exonerate innocent people and narrow a list of suspects. Yes, someone else’s eye could be your alibi.

This all sounds pretty cool, but the images you’re taking with most DSLRs won’t be sharp enough to preserve any facial reflections. The researchers were working with 39 megapixel images, and lighting conditions were optimal. As sensor resolution increases, this technique could become a viable option for law enforcement. However, it isn’t regular cameras that will be the key — cell phone photos are becoming far more common.

Most high-end phones top out at 13MP or so, which is still far short of the resolution needed to recover reflections from the pupil. Still, in a few years the unrelenting march of progress could result in smartphones with cameras that produce images large enough to leak information in the eyes of those you photograph.

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Dozerman

Reminds me of taken where he sees the kidnaper’s face in a reflection behind his daughter and her friend.

Boudou

The researchers used a Hasselblad H2D medium-format digital. Not only does it benefit from 39 megapixels, but it also benefits from a massive sensor and huge lens. Granted, the H2D is a big old, but you could still buy a car for the price of the gear these guys used.

Regardless, its an interesting proof of concept. Its more interesting that a Department of Psychology did this research rather than an engineering dept.

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